Pyrrolobenzodiazepines and Indolinobenzodiazepines
Some pyrrolobenzodiazepines (PBDs) have the ability to recognize and bond to specific sequences of DNA; the preferred sequence is PuGPu. The first PBD antitumor antibiotic, anthramycin, was discovered in 1965 (Leimgruber et al., J. Am. Chem. Soc., 87:5793-5795 (1965); Leimgruber et al., J. Am. Chem. Soc., 87:5791-5793 (1965)). Since then, a number of naturally occurring PBDs have been reported, and over 10 synthetic routes have been developed to a variety of analogues (Thurston et al., Chem. Rev. 1994:433-465 (1994)). Family members include abbeymycin (Hochlowski et al., J. Antibiotics, 40:145-148 (1987)), chicamycin (Konishi et al., J. Antibiotics, 37:200-206 (1984)), DC-81 (Japanese Patent 58-180 487; Thurston et al., Chem. Brit., 26:767-772 (1990); Bose et al., Tetrahedron, 48:751-758 (1992)), mazethramycin (Kuminoto et al., J. Antibiotics, 33:665-667 (1980)), neothramycins A and B (Takeuchi et al., J. Antibiotics, 29:93-96 (1976)), porothramycin (Tsunakawa et al., J. Antibiotics, 41:1366-1373 (1988)), prothracarcin (Shimizu et al., J. Antibiotics, 29:2492-2503 (1982); Langley and Thurston, J. Org. Chem., 52:91-97 (1987)), sibanomicin (DC-102) (Hara et al., J. Antibiotics, 41:702-704 (1988); Itoh et al., J. Antibiotics, 41:1281-1284 (1988)), sibiromycin (Leber et al., J. Am. Chem. Soc., 110:2992-2993 (1988)) and tomamycin (Arima et al., J. Antibiotics, 25:437-444 (1972)). PBDs are of the general structure:

They differ in the number, type and position of substituents, in both their aromatic A rings and pyrrolo C rings, and in the degree of saturation of the C ring. In the B-ring there is either an imine (N═C), a carbinolamine (NH—CH(OH)), or a carbinolamine methyl ether (NH—CH(OMe)) at the N10-C11 position which is the electrophilic center responsible for alkylating DNA. All of the known natural products have an (S)-configuration at the chiral C11a position which provides them with a right-handed twist when viewed from the C ring towards the A ring. This gives them the appropriate three-dimensional shape for isohelicity with the minor groove of B-form DNA, leading to a snug fit at the binding site (Kohn, In Antibiotics III. Springer-Verlag, New York, pp. 3-11 (1975); Hurley and Needham-VanDevanter, Acc. Chem. Res., 19:230-237 (1986)). Their ability to form an adduct in the minor groove, enables them to interfere with DNA processing, hence their use as antitumor agents.
Indolinobenzodiazepines (IBDs) differ from PBDs, in that the PBD C ring is replaced by an indolino ring. For the sake of convenience, certain A ring and B ring positions in the IBDs adopt the same nomenclature as those in the PBDs, such as the C6-C9, N10, and C11 positions.
Antibody-Drug Conjugates
Antibody therapy has been established for the targeted treatment of patients with cancer, immunological and angiogenic disorders (Carter, P. (2006) Nature Reviews Immunology 6:343-357). The use of antibody-drug conjugates (ADC), i.e., immunoconjugates, for the local delivery of cytotoxic or cytostatic agents, i.e., drugs to kill or inhibit tumor cells in the treatment of cancer, targets delivery of the drug moiety to tumors, and intracellular accumulation therein, whereas systemic administration of these unconjugated drug agents may result in unacceptable levels of toxicity to normal cells as well as the tumor cells sought to be eliminated (Xie et al. (2006) Expert. Opin. Biol. Ther. 6(3):281-291; Kovtun et al. (2006) Cancer Res. 66(6):3214-3121; Law et al. (2006) Cancer Res. 66(4):2328-2337; Wu et al. (2005) Nature Biotech. 23(9):1137-1145; Lambert J. (2005) Current Opin. in Pharmacol. 5:543-549; Hamann P. (2005) Expert Opin. Ther. Patents 15(9):1087-1103; Payne, G. (2003) Cancer Cell 3:207-212; Trail et al. (2003) Cancer Immunol. Immunother. 52:328-337; Syrigos and Epenetos (1999) Anticancer Research 19:605-614).
Maximal efficacy with minimal toxicity is sought thereby. Efforts to design and refine ADC have focused on the selectivity of monoclonal antibodies (mAbs) as well as drug mechanism of action, drug-linking, drug/antibody ratio (loading), and drug-releasing properties (Chari, R V J (2008) Acc. Chem. Res., 41:98-107, Junutula et al., 2008b Nature Biotech., 26(8):925-932; Dornan et al. (2009) Blood 114(13):2721-2729; U.S. Pat. No. 7,521,541; U.S. Pat. No. 7,723,485; WO 2009/052249; McDonagh (2006) Protein Eng. Design & Sel. 19(7):299-307; Doronina et al. (2006) Bioconj. Chem. 17:114-124; Erickson et al. (2006) Cancer Res. 66(8):1-8; Sanderson et al. (2005) Clin. Cancer Res. 11:843-852; Jeffrey et al. (2005) J. Med. Chem. 48:1344-1358; Hamblett et al. (2004) Clin. Cancer Res. 10:7063-7070). Drug moieties may impart their cytotoxic and cytostatic effects by mechanisms including tubulin binding, DNA binding, or topoisomerase inhibition. Some cytotoxic drugs tend to be inactive or less active when conjugated to large antibodies or protein receptor ligands.
The present inventors have developed a novel approach to forming PBD conjugates and IBD conjugates with cell binding agents, and in particular PBD or IBD antibody conjugates.